Chapter 41 

 SEALAB II UNDERWATER WEATHER STATION 



E. A. Murray, D. L. Inman, and W. A. Koontz 

 Scripps Institution of Oceanography 

 University of California 

 La Jolla, California 



INTRODUCTION 



An underwater weather station was installed near Sealab II and maintained by the aquanauts. 

 The weather station measured water current, direction, pressure, temperature, and ambient 

 light. It was intended that these measurements provide the divers with the most essential pa- 

 rameters of underwater weather, as well as necessary background information for other sci- 

 entific programs undertaken during the operation. Li addition, it was hoped that the under- 

 water weather station measurements, when compared with similar measurements obtained 

 synoptically elsewhere on the shelf, would provide insight into the complex phenomena that 

 constitute underwater weather. 



There are almost no continuous observations of the underwater environment that are of 

 sufficient scope to be considered as underwater weather. Yet, underwater weather is as im- 

 portant to man in the sea as to man in the atmosphere. The kinds of parameters to be sensed 

 are similar to those in the atmosphere: current speed and direction, pressure, temperature, 

 and light. Their measurement underwater is somewhat more complicated, principally because 

 water is wet. In addition, the underwater environment has greater pressure, viscosity, specific 

 heat, and biological activity of all kinds. The importance of biological activity is frequently 

 overlooked in underwater instrumentation. Every few days, it was necessary to clean organic 

 growth and fouling from the current meters. The current measured underwater appears de- 

 ceptively weak in terms of air currents. However, "gusts" up to nearly two knots were mea- 

 sured near Sealab and these, because of the increased density and viscosity of water, would 

 have exerted a drag on the diver equivalent to that of a 50 to 100 knot wind in the atmosphere. 



Sealab II, with three teams of divers and a total underwater occupancy of 45 days, pre- 

 sented an excellent opportunity to obtain long-period continuous measurements of the under- 

 water environment. 



DESCRIPTION OF THE AREA 



The site of Sealab II was the continental shelf just north of La Jolla, California, where 

 Point La Jolla forms a small hooked bay which opens to the northwest. The shelf area within 

 the embayment is cut by two main branches of La Jolla Submarine Canyon (Fig. 136). Sealab II 

 was placed on the rim of the northern branch, Scripps Submarine Canyon, where the rim has a 

 depth of about 210 ft; the floor of the adjacent canyon has a depth of 650 ft. Both La Jolla and 

 Scripps Canyons extend across the continental shelf and terminate within a few hundred feet of 

 the beach. The shelf between the two canyons is covered with fine sand in shallow water and 

 with fine sand and coarse silt at the Sealab II site (1). Scripps Canyon is narrow and precipi- 

 tous, and in many places the walls are vertical as indicated by observations from the diving 

 saucer (2). 



For many years it has been known that the heads of Scripps Canyon trapped sand from the 

 adjacent beaches. This beach sand is eventually deposited in the deep water of San Diego 

 Trough, some 16 to 20 miles seaward. The mechanism by which the sand is transported through 



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